ArrayList的contains方法，底层调用了equals方法。

/*
思路
1对人描述，将数据封装进人对象
2定义容器，将人存入
3取出
*/
import java.util.*;
class Person
{
private String name;
private int age;
Person(String name,int age)
{
this.name= name;
this.age= age;
}
public boolean equals(Object obj)
{
if(!(obj instanceof Person))
return false;

Person p= (Person)obj;
return this.name.equals(p.name)&& this.age == p.age;
}
public String getName()
{
return name;
}
public int getAge()
{
return age;
}
}

class Test
{
public static void main(String[] args)
{
ArrayList al = new ArrayList();

al.add(new Person("lisi01",30));
al.add(new Person("lisi02",35));
al.add(new Person("lisi03",32));
al.add(new Person("lisi02",35));
al.add(new Person("lisi03",32));
al.add(new Person("lisi04",31));

al=singleElement(al);

Iterator it = al.iterator();

while (it.hasNext())
{
Person p = (Person)it.next();
sop(p.getName()+"---"+p.getAge());
}
}

public static ArrayList singleElement(ArrayList al)
{
//定义一个临时容器
ArrayList newAl = new ArrayList();
Iterator it =al.iterator();

while (it.hasNext())
{
Object obj = it.next();
if (!newAl.contains(obj))
newAl.add(obj);
}
return newAl;
}

public static void sop(Object obj)
{
System.out.println(obj);
}
}

public boolean contains(Object o) {
return indexOf(o) >= 0;
}
public int indexOf(Object o) {
if (o == null) {
for (int i = 0; i < size; i++)
if (elementData[i]==null)
return i;
} else {
for (int i = 0; i < size; i++)
if (o.equals(elementData[i]))    //调用参数的equals方法
return i;
}
return -1;
}